Late Quaternary Glacier response to humidity changes in the arid Andes of Chile (18-29 degrees S)

Today, no glaciers exist between 18 degrees 30 'S and 27 degreesS, even on mountains much higher than 6000 in. These dry high-mountain environments ar e very sensitive to changes in climatic boundary conditions, particularly h umidity since temperatures are far below freezing. Here we present a recons truction of climatic changes since the Last Glacial Maximum for the Chilean dry Andes of the southern hemisphere. We reconstructed regional equilibriu m line altitudes (ELA) for three different moraine stages, representing ext ensive past glaciations in this currently unglaciated region. Comparison of the regional pattern of the ELA with modem climate conditions allows us to draw implications about the paleoclimatic conditions during the best prese rved 'moraine stage II' glaciations in the northern as well as in the south ern part of the research area. Our results suggest humid conditions in the northern part (18-24 degreesS) during Late Glacial times, with strongly inc reased convective precipitation during austral summer. The temporal-coincid ence of glaciers in the mountains and high lake levels on the Altiplano (Ta uca Phase) is evident. To the south, no simple shift of the Westerlies is i mplied by our glacier reconstructions. The northern limit of effective mois ture for glacier formation did not shift significantly, but stayed in the a rea of the present day northernmost glaciers of the Westerlies at about 27 degreesS. But further south, precipitation increased significantly, accompa nied by at least 2-3 degreesC colder conditions. The age of this glaciation is uncertain, but probably of Late Glacial or Last Glacial Maximum (LGM) t imes. Overall, glaciers in the dry Andes of South America clearly responded to large changes in the humidity, not primarily the temperature regime, wi th all its consequences on the environment (hydrology, vegetation, etc.), i llustrating the different regional responses to global climatic change. (C) 2001 Elsevier Science B.V. All rights reserved.